1. Field of the Invention
The present invention relates to a drive state detection circuit, and particularly relates to a drive state detection circuit that detects a drive state of parts driven by alternating currents.
2. Description of the Related Art
CCFLs (Cold Cathode Fluorescent Lamps) are used as, for example, back lights of liquid crystal display monitors. The CCFLs are driven by a drive system with an alternating current. The drive system is equipped with a protection system that detects a drive state of the CCFLs to protect the CCFLs.
The protection system usually detects the drive state of CCFLs by outputting maximum values of the voltage and current supplied to the CCFLs. For outputting maximum values, a protection system disclosed, for example, in Japanese Patent Laid-Open publication No. 6-267674 and No. 2002-134293, holds AC signals of the voltage and current supplied to CCFLs at their peaks, and converts them into DC signals.
State detection circuits for CCFLs with the above type of protection systems therefore need to have additional circuits such as peak hold circuits, which make the configuration complicated.